Virtually all dyes that are classified as anionic in nature prior to the present invention require some levels of salt to influence the dyeing process.
Direct dyes are anionic normally because of sulfonic acid groups which impart water solubility. This class of dye is water soluble, but it also has great affinity for cellulose. The conventional method of application is to put the dye and the fiber (cotton, rayon etc), into a hot water bath, where the fiber swells, and then to add salt into the water to "salt" the dye out of solution. In this manner, the partitioning coefficients are changed to favor the partitioning in the fiber. Once inside the fiber, the temperature is reduced and the dye molecule is merely trapped inside the fiber, although some Van der Waal attraction between the dye and fiber does occur. There is no chemical bond between direct dye and the fiber aside from some weak hydrogen bonding.
Normally acid dyes are used for the dyeing of nylon or wool, defending upon an attachment with cationic amine groups inherent to those fibers. The molecules are much like those in direct dye, but the molecules are usually smaller. Acid dyes are applied in acid conditions at which the amine groups are protonated. Acid dyes are not normally used on cotton because of their size and the fact that the dye molecules can be removed from the fiber so easily after initial dyeing.
Vat dyes exist in two states, a water soluble form and an insoluble form. In use they are converted into the soluble form by reducing them, followed by application to the fiber. They must then be reoxidized. Reoxidation takes the dye to an insoluble state. Since the dye is now within the fiber, it can't be removed as long as it is insoluble thus this class of dye generally has outstanding wet fastness properties. The soluble form or "leuco" form as it is called, is anionic. Sulfur dyes are much like vat dye. They use a different kind of generic molecule having lower purity dyes with less brilliance than other classes. However, they are inexpensive. The sulfur dyes also have a leuco or reduced state which is anionic. It is made soluble prior to dyeing by reduction and insoluble by oxidation after dyeing similar to vat dye.
Fiber reactive dye actually react chemically with cellulose. They are anionic when in a water solution and therefore have affinity to polar fibers such as cellular, wool and the like. The application of this dye conventionally requires extremely high amounts of salt for salting the dye out of solution and into the fiber.
Depending upon the source of the information, direct dyes can be categorized by the way that salt is employed in the dyeing process. The Society of Dyers and Colorist classify dyes into three groups. Group A contain those dyes which have good migrating and leveling properties. Group B contain those dyes that have poor migrating or leveling properties but their dyeing can be controlled by the application of salt during the dyeing process. Group C dyes are those that have poor migrating properties but require good control of both dyeing temperature and salt additions.
Ciba-Geigy classifies Direct dyes into four broad groups according to their salt sensitivity and salt requirements.
Group 1 consists of those that will exhaust 50% or more in the absence of salt but will exhaust almost completely with 5-10 grams/liter (gpl) of salt. (Example--CI Direct Yellow 28)
Group II consists of those that will exhaust 20 to 30% in the absence of salt and progressively increase in exhaustion as the salt concentration is increased to 20 grams/liter. (Example--CI Direct Blue 71).
Group III consists of dye having very low substantivity without salt and only moderately increase their exhaust rate (speed of dyeing) with rising salt concentrations. (Example--CI Direct Green 27).
Group IV consists of dyes which are salt sensitive, (Example--CI Direct Yellow 37).
Crompton and Knowles also divides the dyeing with direct dyes according to salt sensitivity. Their classification: Group A Slow striking dyes requiring large levels of salt for complete exhaustion. Group B Medium striking dyes which require moderates amount of salt for complete exhaustion and Group C which are the rapid striking dyes which are salt sensitive and require little or no salt for light shades.
Salt sensitive dyes will tend to agglomerate excessively leading to poor crock fastness or other problems such as exhausting too quickly in the presence of even small amounts of salt.
It can easily be seen that dyestuffs having large differences in their dyeing behavior when using salt for exhaustion are to be avoided if possible when trying to combine dyes for purposes of matching a shade having the proper mixture of fastness properties. Thus there would be an advantage to the dyer if salt additions were net a factor to be considered in the dyeing process. Further, many more combinations of dyes that the dyer could now choose would be possible. Either common salt (NaCl), or Glauber's Salt(Na.sub.2 SO.sub.4) are the salt of choice for use in the dyeing process.
It is known to use an epoxy ammonium compound having the following formula: ##STR2## wherein R, R',R" and R"' are alkyl radicals having 1 to 8 carbon atoms, and X-- is an anionic group such as the sulfate group, the sulfonate group or a halide group. The halides which may be used are fluoride, chloride, bromide or iodide.
The additive may be utilized in two distinct processes. The epoxy compound may be applied to the textile material within the dyeing bath or the printing pastes, i.e. in the presence of the dyestuff which is to be taken up by the textile material. Also, the fabric prior to carrying out the dyeing process can be treated with the epoxy compound.
It is known to fix the additive to cellulosic materials in the presence of an alkaline substance whose concentration increases inversely with the treatment temperature. In other words, higher concentrations of the alkali are necessary with lower temperatures, and higher temperatures are required when lower concentrations of the alkali are used. Generally, the alkali is a strong base, preferably caustic soda and extremely high concentrations are applied by the prior art to ensure fixation at low temperatures.
However, treatments at elevated temperatures have become preferable to lower temperature treatments utilized in the prior art because of faster processing and higher yields obtainable in industrial equipment.
It is known that treatment of the textile material at high temperature, after it has been impregnated with the epoxypropylammonium salt, gives rise invariably to a strong yellowing thereof. The yellowing may not be removed in the course of the usual treatments.
Such yellowing constitutes a considerable handicap to the use of the epoxypropylammonium salts at high temperatures.
The yellowing modifies or dulls the desired color when dyeing.
U.S. Pat. No. 3,685,953 to Cuvelier et al discloses a process of treating a hydrolyzed polymer such as cellulose with the epoxypropylammonium salt of the invention or the corresponding chlorohydrin and then drying at a high temperature to improve dyeing.
U.S. Pat. No. 3,853,460 to Balland relates to the use of alkylsulfosuccinates and alkylsulfosuccinates with the epoxypropylammonium salts to prevent hydrolysis of the compound to the dihydroxy compound.
U.S. Pat. No. 4,072,464 to Balland relates to the use of boric acid with the epoxypropylammonium salt to improve dye penetration of a cellulosic fabric and to decrease yellowing. The fabric is then heat treated at an elevated temperature.
U.S. Pat. No. 4,035,145 relates to the use of N-(2,3-epoxyalkyl) ammonium salts such as N-methyl-N-(2,3-epoxypropyl)-morpholinium chloride in the presence of alkaline compounds to improve the dyeability of cellulosic textiles.
U.S. Pat. No. 5,006,125 to Patton et al discloses the use of the epoxypropyl ammonium salt or the corresponding chlorohydrin to improve the bleaching process of cellulosic fabrics.
It is understood that the term "cellulosic fabrics" as used herein relates to natural and synthetic fabrics containing free hydroxyl groups which include cotton, flax, linen, rayon, and the like. This process is also useful on other polyhydroxyl polymers such as polyvinyl alcohol.
The term "fabric" as used herein refers to yarns, tows, mats, bathings, cloth, and the like which constitute similar fibers or blends with other natural or synthetic fibers such as wool, polyester, nylon, etc.
It is understood that the term "salt" which Is used herein refers to inorganic salts such as NaCl and Na.sub.2 SO.sub.4 which are used in a dyeing process to increase the speed of the dyeing process.